This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from our two applications ECCENTRIC ROTOR HAVING HIGH DENSITY MEMBER, MANUFACTURING METHOD THEREOF, AND FLAT CORELESS VIBRATOR MOTOR USING THE ECCENTRIC ROTOR filed with the Japanese Patent Office on Jun. 29, 2001, and duly assigned serial Nos. 2001-199603 and 2001-199604.
1. Technical Field
The present invention relates to an eccentric rotor having a high density member for a vibrator motor as a silent call means of a portable communications device, a manufacturing method thereof, and a flat coreless vibrator motor using the eccentric rotor.
2. Related Art
As silent call means of portable communications devices such as pagers or mobile phones, as shown in FIG. 8, an eccentric weight W formed of tungsten alloy is arranged at an output shaft S of a cylindrical DC motor M and vibration is generated by using a centrifugal force of the eccentric weight W during rotation.
However, adding the eccentric weight W at the output shaft S as above limits its design due to a space in which the eccentric weight W rotates. Also, since tungsten alloy which is expensive is used, a manufacturing cost increases.
Thus, the present applicant proposed to remove the output shaft and make the included rotor itself eccentric. A flat motor is disclosed in Japanese Patent Publication No. hei 8-10972 (U.S. Pat. No. 5,036,239 and Canada Patent No. 2,017,395). A cylindrical coreless vibrator motor is disclosed in Japanese Patent Application No hei 2-309070 (U.S. Pat. No. 5,107,155).
In these motors, since no output shaft and eccentric weight are provided, there is no limit to design, it is easy to use, and no danger exists during rotation.
Since an output shaft is not needed, the vibrator motor including an eccentric rotor is a so-called shaft fixed type motor in which a shaft is fixed to a housing. The shaft fixed type motor is proposed by the present applicant in Japanese Patent Publication No. hei 6-81443 and Japanese Patent No. 2,872,623.
Since the above motors have very thin coreless coils, they should be handled carefully. Also, since all the motors need molding processes, the number of parts or processing steps increase.
Recently, as portable devices are made smaller, more compact vibrator motors are required. For a flat type motor, a motor having a diameter less than 10 mm is required. With the above size motor, a sufficient vibration amount cannot be obtained since the amount of movement of the center of gravity in a radial direction obtained by simply making air-core armature coils eccentric is not great.
As a result, a resin which has a high density by increasing the amount of mixture of tungsten alloy must be used. However, in this case, since a value of resistance of a resin portion is lowered, unnecessary current flows through the resin portion and thus consumption of current increases.
To solve the above-described problems, it is an object of the present invention to provide an eccentric rotor having a high density member suitable for a vibrator motor which is ultra-compact and simultaneously provides a great amount of movement of the center of gravity in a radial direction so that a desired vibration amount can be obtained and further secures insulation between an air-core armature coil or printed wired commutator and resin so that consumption of current is not scarified while employing a high density member comprising metal.
It is another object of the present invention to provide a method of manufacturing the above eccentric rotor.
It is yet another object of the present invention to provide a flat coreless vibrator motor adopting the above eccentric rotor.
It is still an object of the present invention to provide a bearing for the rotor having a low coefficient of dynamic friction.
To achieve the above object, there is provided an eccentric rotor having a high density member comprising a rotor base having an air-core armature coil installation surface, a bearing holder provided at a center thereof, and an air-core armature coil position determination guide formed of a high density member including metal, having a specific gravity of 6 or more and arranged to be eccentric outside of the bearing holder, an air-core armature coil arranged at the air-core armature coil position determination guide, a printed wired commutator member installed to insulate a conductive portion having electric potential from the high density member, and an end connection pattern, in which ends of the air-core armature coil are connected, installed at the printed wired commutator member inside an outer circumference of rotation at a position not overlapping the air-core armature coil. In this case, a desired amount of vibration can be obtained by sufficiently securing the amount of movement of the center of gravity in a radial direction while the eccentric rotor is ultra-small.
In the first embodiment of the present invention, the bearing holder and the air-core armature coil position determination guide are formed of resin including tungsten alloy, having a density of 6 through 10 and a dynamic friction coefficient of 0.5 (1.5 kg/cm2) or less, and the resin itself functions as a bearing. In this case, the resin itself can work as a bearing. Accordingly, it is unnecessary to provide with an additional bearing.
In the second embodiment of the present invention, the bearing holder and the air-core armature coil position determination guide are formed of resin including tungsten alloy, having a density of 6 or more, and an additional bearing is arranged at a center of the bearing holder. In this embodiment, an eccentric rotor having a low dynamic friction coefficient can be realized while using a bearing holder having a high specific gravity and a high density. In this embodiment, the additional bearing is a metal sintered oilless bearing which is integrally formed with the bearing holder.
It is preferred in the present invention that the air-core armature coil position determination guide guides by using an inner or outer diameter of the air-core armature coil, and an air-core armature coil end guiding portion of the air-core armature coil is provided inside the outer circumference of rotation. In this case, the determination of the position of the air-core armature coil is made easy and a problem of disconnection of the end of the air-core armature coil does not occur.
To achieve the second object according to the first embodiment of the present invention, there is provided a method of manufacturing an eccentric rotor comprising the steps of molding a rotor base which includes an air-core armature coil installation surface, a bearing holder at a center thereof, and an air-core armature coil position determination guide formed of a high density member, including metal having a specific gravity of 6 or more and arranged to be eccentric outside of the bearing holder, arranging the air-core armature coil at the air-core armature coil position determination guide, installing a printed wired commutator member at the rotor base such that a conductive portion having electric potential is insulated from the high density member, connecting ends of the air-core armature coil to an end connection pattern installed at the printed wired commutator member and inside an outer circumference of rotation at the position not overlapping the air-core armature coil.
To achieve the second object according to the second embodiment according to the present invention, the above eccentric rotor can be manufactured by a method which comprises the steps of forming an eccentric rotor base by integrally molding a bearing holder at a center thereof and an air-core armature coil position determination guide outside the bearing holder by using a high density member including metal having a specific gravity of 6 or more which is the same as the bearing holder, arranging a sintered oilless bearing at the center of the rotor base, inserting an air-core armature coil around the air-core armature coil position determination guide, installing a printed wired commutator member such that a conductive portion having electric potential does not contact the rotor base, and connecting ends of the air-core armature coil to an end connection pattern installed at the printed wired commutator member and inside an outer circumference of rotation at the position not overlapping the air-core armature coil.
To achieve the third object, there is provided a flat coreless vibrator motor comprising an eccentric rotor comprising a rotor base having an air-core armature coil installation surface, a bearing holder provided at a center thereof, and an air-core armature coil position determination guide formed of a high density member, including metal having a specific gravity of 6 or more and arranged to be eccentric outside of the bearing holder, an air-core armature coil arranged at the air-core armature coil position determination guide, a printed wired commutator member installed to insulate a conductive portion having electric potential from the high density member, and an end connection pattern, in which ends of the air-core armature coil are connected, installed at the printed wired commutator member inside an outer circumference of rotation at a position not overlapping the air-core armature coil, a magnet installed to face the eccentric rotor with a gap, a brush arranged inside the magnet for providing electric power to the eccentric rotor, a shaft for rotatably supporting the eccentric rotor, and a housing for housing the eccentric rotor, the magnet, the brush, and the shaft.
It is preferred in the present invention that the eccentric rotor is assembled such that the air-core armature coil faces the magnet.